The aim of this study is to investigate how the efficacy and tolerability of PD P 506 A-PDT relate to the commonly used cryosurgery in the treatment of mild to moderate AK lesions located on the head. To be able to quantify the effect the patient will be allocated to one of three treatments: PD P 506 A-PDT, cryosurgery or placebo-PDT.

Actinic keratosis (AK) is a pre-cancerous skin abnormality usually caused by sun exposure. Actinic keratoses occur most commonly in fair skin, especially in the elderly. They mainly occur in sun-exposed skin areas like head and hands. It is standard of care to remove AK when diagnosed, which can be achieved by either physical ablation, chemotherapeutic agents or photodynamic therapy (PDT). In Europe, cryosurgery is the method primarily used and will therefore serve as comparator therapy for PD P 506 A-PDT. A placebo control will be necessary to validate the test system. While the comparison of PD P 506 A-PDT and cryosurgery is an open comparison, placebo-PDT and PD P 506 A-PDT will be allocated in a double-blind manner.

Inclusion Criteria:

• Written informed consent
• Caucasians
• Age > 18 years
• Diagnosis of actinic keratosis (AK) with at least four locally separated lesions located on head and/or face (hairless areas)
• Selected AK study lesions have clearly defined margins and are mild to moderate (grades I or II)
• The distance between the study lesion borders is > 1.0 cm
• Maximum diameter of each study lesion is 1.8 cm
• Skin sun sensitivity type I to IV according to Fitzpatrick

Exclusion Criteria:

• PDT Non-responder
• Pre-treatment of the AK lesions eligible for study procedures with pharmaceuticals approved for the treatment of AK during the 4 weeks preceding study treatment
• Pre-treatment of the AK lesions eligible for study procedures during the 2 weeks preceding study treatment with keratolytic agents e.g. TCA, urea or salicylic acid containing formulations
• Pre-treatment with hypericin during the 2 weeks preceding study therapy
• Treatment with systemic retinoids during the 3 months preceding study therapy
• Treatment with cytostatics or radiation during the 3 months preceding study therapy
• Female patients of childbearing potential
• Patients with clinically relevant suppression of the immune system
• Diagnosis of Porphyria
• Skin diseases that might interfere with response evaluation of study treatment
• Skin sun sensitivity type V or VI according to Fitzpatrick
• Known intolerance to one or more of the ingredients of the study medication
• Known adverse reactions to cryosurgery (including cold urticaria and cold intolerance)
• Dementia or psychic condition that might interfere with the ability to understand the study and thus give a written informed consent
• Simultaneous participation in another clinical study or participation in another clinical study in the 30 days directly preceding inclusion
• Suspected lack of compliance